Contracts Accounted for as Credit Derivatives - Narrative (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	10 years 2 months 4 days	5 years 3 months 6 days
Net par outstanding	$ 7,535	$ 16,997
Collateral Debt Obligations, Collateral Cap Negotiated [Member]
Credit Derivatives
Gross par of contracts expected to be terminated		183
Collateral already posted being terminated		73
Market value collateralized debt obligations of corporate obligations [Member]
Credit Derivatives
Average obligor size (less than)	1.00%
Maximum exposure of one industry (as a percent)	10.00%
Net par outstanding	$ 1,644	$ 10,425